This invention relates to a vacuum heat treating furnace and quench tank system having a system for quickly moving the workpiece from the heat chamber to the quench tank.
Heat treat furnace and quench tank systems in which metals are heated and then quenched in a liquid to obtain a rapid cool of the metal are known in the art. The heat treatment of metals is generally defined as a combination of heating and cooling operations timed and applied to a metal or alloy in the solid state in a way that will produce desired properties.
U.S. Pat. No. 3,429,563 to Anderson et al and U.S. Pat. No. 3,522,357 to Pine et al are two examples of heat treating furnaces and quench tank structures.
The vacuum heat treat furnaces and particularly those with liquid quench mediums are currently being developed and applied more extensively. They provide some unique and extreme capabilities not obtainable in conventional heat treat furnaces. These vacuum heat treat furnaces can easily operate at temperatures to 3000.degree. F. and above and to vacuum levels of 10.sup.-7 mm Hg. and below.
These vacuum heat treat furnaces are cycled from ambient conditions to operating temperature and vacuum levels repeatedly. Many difficulties are encountered during operation. It is a problem to provide a reliable and quick transfer of the load or workpiece to the quench medium. It is also a problem to achieve and maintain a vacuum environment that is constant and free of contaminents, and to keep both the internals of the furnace and the parts being heat treated free from foreign material and contamination.
A common problem encountered with prior art devices results from the vaporization of some of the quench liquid which would occur when, for example, a load is placed in the quench. The subsequent condensation and deposition of the liquid vapor on not only furnace interior parts, but also, on load parts being heat treated contaminates the load and results in the derogation of the heat treating process. This is particularly true of liquid mediums, such as water, that have comparatively high vapor pressures, and is also true of quench oils with substantially lower vapor pressures. In some of the prior devices there is direct line of sight exposure between the heating zone chamber and the liquid quench surface throughout the quench period. These extended periods of open unobstructed passageways between heating zone chamber and liquid quench surface permits and promotes vapor movement.
Another frequent source of contamination is the alternate exposure of furnace operating parts to the quench liquid and then directly to the furnace heating zone interior. Typical examples of such furnace operating parts are load support rails, elevator and hoist parts, chains, cables and hooks. These parts move from the heating zone chamber to the quench chamber and then return to the heating zone chamber as they convey workpieces from the heat treatment to the quench. This source of contamination is especially troublesome with liquid mediums of comparatively low vapor pressures, such as oil.
In many of the prior art devices there is extensive use of mechanical linkages, components and motions to transfer the load between the heating zone and the quench tank. These complicated mechanisms are not only a source of mechanical operating problems, but also impose an undesirable time lag between the end of heat and quench.
The problems outlined above have been known, experienced and tolerated, for many years, and have been accepted as characteristic of vacuum heat treat equipment. Although there has been continuous effort, for many years, by the heat treating industry, to circumvent and solve these problems, there has been no complete solution to date. My invention solves these problems.